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首页> 外文学位 >HEAT AND MASS TRANSFER IN POROUS MEDIA IN CONVECTIVE HEATING AND/OR MICROWAVE HEATING.
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HEAT AND MASS TRANSFER IN POROUS MEDIA IN CONVECTIVE HEATING AND/OR MICROWAVE HEATING.

机译：对流加热和/或微波加热中多孔介质的传热和传质。

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摘要

Drying consumes a large amount of energy and is a limiting step in industrial production. To cut down production cost and to improve the quality of products, it is important to study the effect of external heating conditions on the evaporation rate and the internal mechanisms of the heat and mass transfer in the heated products. This thesis is devoted to explore these two research areas.;In an experimental study of heating conditions a water-filled cylindrical sandstone was heated by hybrid energy (convective hot air and/or microwaves) in a sequence of increasing heating intensity. As the heating intensity increases, the evaporation rate increases and the evaporation-rate curve undergoes a series of shape changes. Based on the drying phenomena of the sandstone, an attempt was made to search optimum heating conditions for a cylindrical bovine muscle.;To investigate the heat and mass transfer mechanisms operative in porous media subjected to convective heating or microwave heating, we solved two slightly different mathematical models for the cylindrical sandstone. For the convective heating, the sample is hotter outside. In most of the heating period, water vapor condenses along its path as it flows toward the centerline of the sample and air also moves in the same direction but at smaller flux. Liquid water, however, migrates toward the surface with a flux 2 to 3 orders of magnitude larger than vapor flux. As for the microwave heating, the sandstone is hotter inside. During most of the heating period, air slowly flows to the sample's centerline, water vapor flows to the surface, and liquid vaporizes as it flows to the surface with higher flux than vapor.;For the first research area, a capillary-tube model was solved to examine the influence of mass transfer coefficient, sample temperature, and liquid front depth on the evaporation rate. It is found that the effect of front depth on the evaporation rate becomes increasingly significant and approaches a limit for mass transfer coefficients larger than 5 cm/sec, but this effect becomes insignificant for mass transfer coefficients much lower than 5 cm/sec.
机译：干燥消耗大量能量，并且是工业生产中的限制步骤。为了降低生产成本并提高产品质量，重要的是研究外部加热条件对加热产品中蒸发速率的影响以及内部传热和传质机理。本论文致力于探索这两个研究领域。在加热条件的实验研究中，用混合能量（对流热空气和/或微波）按加热强度递增的顺序加热了充满水的圆柱形砂岩。随着加热强度的增加，蒸发速率增加，并且蒸发速率曲线经历一系列形状变化。基于砂岩的干燥现象，试图寻找圆柱状牛肌肉的最佳加热条件。为了研究在对流加热或微波加热下多孔介质中的传热和传质机理，我们解决了两个略有不同的问题圆柱砂岩的数学模型。对于对流加热，样品在室外较热。在大多数加热期间，水蒸气流向样品中心线时会沿其路径冷凝，空气也沿相同方向移动，但通量较小。然而，液态水以比蒸气通量大2至3个数量级的通量向表面迁移。至于微波加热，砂岩内部较热。在加热的大部分时间里，空气缓慢流向样品的中心线，水蒸气流向表面，液体以比水蒸气更高的通量流向表面，从而蒸发。对于第一个研究领域，毛细管模型是解决方案，以检查传质系数，样品温度和液体前沿深度对蒸发速率的影响。已经发现，前部深度对蒸发速率的影响变得越来越显着，并且接近大于5 cm / sec的传质系数的极限，但是对于远低于5 cm / sec的传质系数，这种影响变得微不足道。

著录项

  • 作者

    WEI, CHENKOU.;

  • 作者单位

    University of Minnesota.;

  • 授予单位 University of Minnesota.;
  • 学科 Engineering Chemical.
  • 学位 Ph.D.
  • 年度 1984
  • 页码 213 p.
  • 总页数 213
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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